Polyethylene terephthalate homopolymers and copolymers are characterized by excellent physical properties which make them materials of great interest for use in films, fibers and molding applications. Reinforcing materials such as glass fibers are frequently incorporated in order to improve the mechanical properties of the final products prepared from polyethylene terephthalate.
It has been found, however, that the relatively slow rate of crystallization of polyethylene terephthalate and the copolymers thereof greatly limits the use of such polyester composition in injection molding processes. Hence, a great deal of effort has been expended on the discovery of promoters which will accelerate the crystallization rate of polyethylene terephthalate and of its copolymers. Among the various patents which have issued on the accelerations of polyethylene terephthalate and which discuss the efforts of the prior art to overcome the crystallization rate disadvantages of these polyesters there may be mentioned U.S. Pat. Nos. 3,673,139; 4,098,845; 4,107,149; and 4,136,089. In addition, mention can be made of British Pat. No. 1,505,599 and German Pat. Nos. 2,545,720; 2,653,120; 2,706,123; 2,706,124; and 2,706,128. As is evident from these aforementioned patents, the efforts of the prior art have concentrated on the development of specific additives or promoters which will enhance the crystallization rates of polyethylene terephthalate homopolymers and copolymers. However, the rigorous demands of injection molding procedures and the economic factors involved in this field of technology are such that the provision of further means for enhancing the crystallization rates of such polyesters is constantly encouraged.